I want another chicken house. It's going inside another building, so it need not be waterproof or have a floor or base. I was thinking of something modular and plastic that could be taken apart and hosed off if it gets redmite, and I have a seemingly unending supply of polycarbonate-type roofing material.

Design concept is very straightforward. I fix it together into a square and add perches (it would need to be either openable, or able to lift up completely for ease of cleaning). Implementation presents more problems, as in how is one supposed to fix it together?! A wood frame would defeat the object rather.

Hive mind solutions? Or shall I just buy a shed and not felt it instead?

if you fancy a scrap heap challenge the poles from an old and largish frame tent , a bit of scaffolding netting for the dark ,cosy bit, a roll of paracord and some cable ties for attaching stuff are a very good start to creating an "indoor" chook enclosure, perches ,lay boxes etc are easily improvised

for a rustic look a geodesic bender from hazel rods with a scaff netting/ chook wire skin might be fun and with a few fixings to hold it down could be very charming and practical. if it was made in modular sections so as it could be moved in say 6 slices a few cable ties to replace each time would be tidy. a few double frame/cable tie offset overlap joints is a small price to pay for mobility.

I'm rubbish at scrapheap challenge. I just don't have enough experience with making things.

I was thinking of a shed, but I think all that weatherboard would be a nightmare if it got redmite. I don't think I have the space for a bender footprint (also it's a concrete floor)

My other brainwave is a fabricated metal framework that I could just slide panels into. Except it would probably cost more than a shed. And I would have to go and talk to a fabricator who would think I was bonkers. I sometimes get a bit fed up of convincing people that yes, I've really thought about it, and yes, that really is what I want. No, I realise that most people don't. I'm not most people. It gets so exhausting.

Then I thought of polycarbonate greenhouse. It's not going to blow away in the garage, would be relatively modular, washable and fox proof. A 6x6 would be about £200, which is a fifth of the price of an equivalent chicken house. It will come with instructions, and I should be able to put the thing together myself. I would have to rig up some perches and nest boxes, but how hard can that be? Staging would probably work, even. If it doesn't work I can take it out and grow stuff in it. They even have automatic ventilators. I realise chickens outside would overheat in the sun, but this is not an issue in the garage. I don't suppose the insulation bit matters, either.

Good idea. Old greenhouses without glass are available cheap/free. They come with a ready made door. And light enough to drag out and wash.
Polycarbonate sheeting could just be laid over/inside frame and cable tied on. Simple ....assuming an apex roof greenhouse fits inside the garage - although just the walls could be used.

WW by polycarbonate sheeting do you mean the 'twinwall' flat stuff or corrugated ? The former, for your purposes, being easier to work with.

I've no idea. Probably both, as I have two kinds. It's amazingly useful except it isn't strong enough to walk on, and I have not yet dared try cutting it or screwing holes through it.

I've a feeling that there is an old greenhouse frame kicking about somewhere, too. Its bound to be to be the wrong size, so I suppose I'd better figure out how to cut the roofing (it's like thick corrugated cardboard, only fairly brittle plastic. I have other stuff which is clear, and much thicker, perhaps three inches which looks like plastic conservatory)

chooks need plenty of ventilation, they are well dressed for chilly but damp and stuffy is very bad for them.

if you start with a frame of some sort chook wire is cheap, fairly fox proof, easy to attach (cable ties are good ) and nicely drafty .

lay box and roost ark can be very simple as can food , water etc.

as to foxey a visit to the interesting bit of an "indoor" chook pen could be a whole wide world of electric pain if planned with a nasty imagination and a few quid done well it reduces the need for expensive mechanical exclusion of radjel.

problems from rats n woosels etc can be reduced at the design stage but a concrete floor is a good start.

... and I have not yet dared try cutting it or screwing holes through it.

Take whatever saw you have and try it. It will cut it, how badly it damages it - there's only one way to find out.
General rule is gently with a fine tooth saw. Make sure sheet is firmly supported and held when you cut it.

Jigsaw will work but can have a tendency to 'grab' and damage the sheet if you go too gung-ho.

My personal choice is 4inch grinder with a thin diamond blade.

Drilling - use a HSS(metal) bit.

Trial and error - try it - if it works that's fine, if not, go finer/gentler/smaller.

seconded, the use of clamps and planks as well as a big flat surface helps a lot.

disc can be ace with some sorts and a bit "melty" with others
a fine tooth hand saw can be an effective tool if you get the angle of attack right .
if using a jigsaw fine teeth, medium speed , a firm downward pressure against a well secured sheet and a fairly slow cut along the line works best.
cutting through a line of masking tape helps with some types.
cutting between two pairs of parallel lines scored both sides of the sheet with a stanley knife at twice saw cut width spacing can be very effective at reducing splits etc

there are many types of plastic panel ranging from thin acrylic to big compartment triple wall polycarbonate , all need slightly different cutting techniques , the best general rule is firm but gentle using fine teeth

when you have identified what you are going to use show and tell so as we can suggest some options from your toolkit